Miniature,multiturn trimmer potentiometer



Sept. 23, 1969 e. w. wooo 3,469,225

MINIATURE, MULTITURN TRIMMER POTENTIOMETER Filed March 12, 1968 FIG.

[NYE/V701? GEORGE 0% W000 Arron/v0 United States Patent 3,469,225 MINIATURE, MULTITURN TRIMMER POTENTIOMETER George W. Wood, Hammonton, N.J., assignor to TRW Inc., Philadelphia, Pa., a corporation of Ohio Filed Mar. 12, 1968,'Ser. No. 712,486 Int. Cl. H01c /02 US. Cl. 338-163 4 Claims ABSTRACT OF THE DISCLOSURE A miniature, multiturn trimmer potentiometer comprising a cup-shaped housing having an annular resistance path and a contact termination on the inner surface of the base thereof. Terminal pins extend through the base of the housing and are individually connected to the ends of the resistance path and the contact termination. A circular contact carrier plate is mounted in the housing for rotation about its center. The contact carrier. plate carries a contact which slidably engages both the resistance path and the contact termination. A cover extends'across the open end of the housing and is rotatably supported there on. A small gear is secured to the center of the inner surface of the cover and the housing has a ring of gear teeth extending around the gear on the cover. An idler gear is rotatably supported on a pin on the contact carrier plate and meshes with the gear on the cover and the gear teeth on the housing. Rotation of the cover rotates the contact carrier plate through the idler gear with the contact carrier plate rotating at a rate smaller than the rate of rotation of the cover.

Background One type of miniature trimmer potentiometer presently available is shown in United States Letters Patent No. 3,096,499, issued July 2, 1965, to M. W. Hudson et al., entitled Variable Resistor and United States Letters Patent No. 3,354,418, issued Nov. 21, 1967, to H. B. Casey et al., entitled Variable Resistor. This type of trimmer potentiometer in general comprises a cup-shaped housing having three terminals extending through the bottom of the housing. A resistance element is mounted in the housing on the bottom of the housing and has a circular resistance path. Two of the terminals are connected to the ends of the resistance path and the third terminal is connected to a contact termination member on the center of the bottom of the housing. A knob extends across the open end of the housing and is rotatably mounted thereon. The knob carries a contact which slidably engages both the resistance path and the contact termination member. As the knob is rotated, the contact moves along the resistance path to vary the resistance value of the potentiometer. One revolution of the knob moves the contact along the full length of the resistance path.

One problem with this type of trimmer potentiometer is that it is relatively difficult to achieve a desired setting of the contact along the resistance path since the amount of movement of the contact is equal to the movement of the knob. There are types of potentiometers, different and more complex in construction from that described above, which permit far greater ease of achieving a desired setting of the contact by requiring a greater movement of the knob to achieve a desired movement of the contact. Such potentiometers are referred to as multi-turn potentiometers since they require a plurality of revolutions 3,469,225 Patented Sept. 23, 1969 v entire length of the resistance path. Therefore, it would be desirable to have a miniature trimmer potentiometer of the type described above which is a multiturn potentiometer.

Summary of invention It is an object of the present invention to provide a novel miniature, trimmer potentiometer.

It is another object of the present invention to provide a novel miniature, multiturn trimmer potentiometer.

It is a further object of the present invention to provide a miniature trimmer potentiometer having a gearing arrangement between the knob and the contact so that a given movement of the contact along the resistance path requires a greater movement of the knob but the gearing arrangement does not substantially increase the size of the potentiometer.

Other objects will appear hereinafter.

Brief description of drawing For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a transverse sectional view of the trimmer potentiometer of the present invention.

. FIGURE 2 is a sectional view taken along line 22 of FIGURE 1.

FIGURE 3 is an exploded perspective view of the trimmer potentiometer of the present invention.

Description of invention Referring to the drawing, the potentiometer of the present invention is generally designated as 10.

Potentiometer 10 comprises a housing 12 of an electrical insulating material, such as a plastic. Housing 12 has a circular base 14 and a cylindrical wall 16 integral with and extending from the edge of the base 14. In the miniature potentiometer 10 of the present invention, the base 14 may be as small as one-half inch in diameter, and the cylindrical wall 16 approximately one-quarter inch in length.

The cylindrical wall 16 has a cylindrical recess 18 in its outer surface extending from the free edge of the wall. The cylindrical surface of the recess 18 has a cylindrical groove 20 therein adjacent the radial surface of the recess 18. A ring of gear teeth 22 is provided on the inner surface of the cylindrical wall 16 at the free end of the wall. The gear teeth 22 may either be molded as part of the cylindrical wall 16 or may be formed on a separate ring which is molded into the cylindrical wall. An annular ledge 24 is provided on the inner surface of the cylindrical wall 16 just below the gear teeth 22. Three terminal pins 26 extend through and are secured to the base 14 of the housing.

A resistance element, generally designated as 28, is mounted on the base 14 within the housing 12. As shown, the resistance element 28 is of the type shown and described in United States Letters Patent No. 3,354,418, issued Nov. 21, 1967, to H. B. Casey et al., entitled Variable Resistor. The resistance element 28 comprises a relatively thin, flat circular disk 30 of an electrical insulating material, such as a glass, ceramic or plastic. A substantially annular resistance path 32 is provided on the top surface of the disk 30 and extends around the periphery of the top surface of the disk. The resistance path 32 does not 3 l. extend completely around the disk but has spaced apart ends. The resistance path 32 comprises a film of any wellknown resistance material, such as carbon or a metal either with or without a suitable binder. A contact termination 34 is provided on the top surface of the disk 30 at the center thereof. The contact termination 34 comprises a film of an electrically conductive material, such as a metal, coated on the surface of the disk 30.

The terminal pins 26 extend through holes in the resistance element disk 30. Two of the terminal pins 26 are located at the ends of the resistance path 32. The third terminal pin 26 is located adjacent the contact termination 34. The terminal pins 26 are electrically connected to the ends of the resistance path 32 and the contact termination 34 by a suitable electrically conductive cement or solder.

Although the potentiometer is shown as having a resistance element 28 with a film type resistance path instead, it may have a wire-wound type of resistance element. Such a resistance element is shown and described in United States Letters Patent No. 3,096,499, issued July 2, 1963, to M. W. Hudson et al., entitled Variable Resistor. As shown in said Patent No. 3,096,499, a wire- Wound resistance element comprises an annular core of an electrical insulating material having a resistance wire helically wound therearound along substantially the entire length of the core. The resistance element is seated on the inner surface of the base of the housing adjacent the inner surface of the cylindrical wall and the ends of the resistance wire are connected to two of the terminal pins. For a wire-wound type of resistance element, the contact termination may be a thin metal plate secured to the center of the inner surface of the housing base.

Referring again to the drawings, a thing, flat, circular contact carrier plate 36 of an electrical insulating material, such as a plastic, is provided within the housing 12. The contact carrier plate is seated on the ledge 24 on the inner surface of the cylindrical wall 16 and can rotate about its center. A short pin 38 extends from the upper surface of the contact carrier plate 36 and is positioned between the center and the edge of the plate. A contact member 40 of an electrically conductive metal is secured to the bottom surface of the contact carrier plate 36 at substantially the center of the plate. The contact member 40 has a spring arm 42 which exends downwardly to the resistance path 32 of the resistance element 28 and a finger 44 on the end of the spring arm 42 slidably engages the resistance path 32. A second spring arm 46 extends downwardly from the contact member 40 toward the contact termination 34. A finger 48 on the end of the spring arm 46 slidably engages the contact termination 34.

A circular cover 50 of an electrical insulating material, such as a plastic, extends across the open end of the housing 12. The cover is of the same diameter as the diameter of the housing 12. A cylindrical flange 52 extends downwardly from the edge of the cover 50 and fits in the recess 18 in the cylindrical wall 16 of the housing 12. The flange 52 has a circular rib 54 on its inner surface which fits in the groove 20 in the cylindrical wall 16 of the housing 12. The rib 54 is of a size with respect to the groove 20 that it secures the cover 50 to the housing 12 but permits rotation of the cover with respect to the housing. The cover 51 has a transverse slot 56 in its outer surface which is adapted to receive a screwdriver or a similar tool to rotate the cover with respect to-the housing 12. A small gear 58 is secured to the inner surface of the cover 56 at the center thereof. The gear 58 may be molded as an integral part ofthe cover 50 or may be a separate element secured to the cover.

An idler gear 60 is provided between the cover 50 and the contact carrier plate 36 and is rotatably mounted on the pin 38 on the contact carrier plate. The idler gear 60 is of a diameter to mesh with the teeth of the gear 58 on the cover 50 and with the teeth 22 on the inner surface of the cylindrical wall 16 of the housing 12.

In the operation of the trimmer potentiometer 10 ot the present invention, rotation of the cover50 with respect to the housing 12 rotates the gear 58 on the cover. This, in turn, rotates the idler gear 60. Since the idler gear 60 meshes with the teeth 22 on the housing 12, the idler gear 60 not only rotates about the pin 38 but also rotates around the axis of rotation of the cover 50 in a planetary manner. As the idler gear 60 rotates about the axis of rotation of the cover 50, the idler gear 60 engages the pin 38 and causes the contact carrier plate36 to rotate about its center. Rotation of the contact carrier plate 28 moves the finger 44 of the contact arm 42 along the resistance path 32 so as to vary the resistance value between the contact termination terminal pin and the other two terminal pins.

The rate of rotation of the contact carrier plate 36 is equal to the rate of rotation of the idler gear 60 around the axis of rotation of the cover 50. This rate of rotation with regard to the rate of rotation of the cover 50 is a function of the ratio of the number of teeth on the gear 58 to the number of teeth 22 on the housing 12. Since the number of teeth 22 on the housing 12 is much greater than the number of teeth of the gear 58, the rate of rotation of the contact carrier plate 36 is smaller than the rate of rotation of the cover 50. Therefore, one revolution of the cover 50 rotates the contact carrier plate 36 only a fraction of a revolution so that a multiple number of revolutions of the cover are required to move the contact arm finger 44 along the entire length of the resistance path 32. Thus, there is provided a miniature trimmer potentiometer of round configuration which has a multiturn action so as to permit the achievement of fine adjustments of the resistance value of the potentiometer but without substantially increasing the size of the potentiometer.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. A miniature, multiturn trimmer potentiometer comprising:

a cup-shaped housing having a base and an outer wall;

a resistance element mounted in said housing, said resistance element having an annular resistance path with spaced ends;

a contact termination in said housing;

two terminals extending through the housing, one of said terminals being electrically connected to an end of the resistance path, the other terminal being electrically connected to said contact termination;

a contact carrier plate mounted in said housing for rotation with respect to said housing;

a contact member carried 'by said contact carrier plate for rotation therewith, said contact member slidably engaging the resistance path and the contact termination;

a cover extending across and rotatably supported on said housing; and

means drivingly connecting said cover to said contact carrier plate so that the rate of rotation of said contact carrier plate is less than the rate of rotation of said cover.

2. A trimmer potentiometer in accordance with claim 1 in which the drive means between the cover and the contact carrier plate is a series of meshing gears.

3. A trimmer potentiometer in accordance with claim 2 in which the gear drive means between the cover and the contact carrier plate comprises a gear on the center of the inner surface of the cover, a ring of gear teeth on the inner surface of the wall of the housing, and an idler gear between and meshing with the gear on the cover and the gear teeth on the housing, and said idler gear is connected to said contact carrier plate so that, as the idler gear rotates around the gear on the cover, the idler gear rotates the contact carrier plate.

4. A trimmer potentiometer in accordance with claim 3 in which a pin extends from the contact carrier plate toward the cover, said pin being spaced from the center of the contact carrier plate, and the idler gear is rotatably mounted on said pin.

6 References Cited UNITED STATES PATENTS 3,129,382 4/1964 Scott 338118 XR 3,353,074 11/1967 Mittler et al. 338-162 XR 3,388,365 6/1968 Wood 338--162 LEWIS I-I. MYERS, Primary Examiner T. I. KOZMA, Assistant Examiner 

